Commercial methanol plants produce methanol in several steps, usually including synthesis gas preparation (reforming), methanol synthesis and methanol purification. Since these steps are conducted in separate process sections, the technology for each section can be selected and optimised independently. The usual criteria for the selection of technology are capital cost and plant efficiency. The preparation of synthesis gas and compression typically accounts for about 60% of the total investment, and almost all energy is consumed in this process section. Therefore, the technology to produce synthesis gas is of major importance.
The synthesis gas for the production of methanol is usually obtained by subjecting a desulfurised hydrocarbon feed to steam reforming (SR) at a temperature from 800 to 950° C. in the presence of a fixed bed of catalyst, typically containing nickel. The resulting synthesis gas is cooled and compressed to be used further in the methanol process. However, the synthesis gas obtained in steam reforming is usually characterised by a too low carbon/hydrogen ratio compared to a stoichiometric composition optimal for methanol synthesis. As a result, the methanol synthesis reactor typically operates at a large hydrogen excess which results in the overall low plant efficiency.
To adjust the composition of the synthesis gas used for methanol production, a combination of technologies can be used. A method for methanol production known as Combined Reforming Technology (CRT) is described in EP 0233076. Herein, a hydrocarbon feed is split into two feedstock fractions, of which one fraction is subjected to primary steam reforming and is then combined with the second feedstock fraction. The resulting mixture is reacted with an oxygen containing gas in a secondary reforming reactor. The resulting raw synthesis gas is mixed with a hydrogen-rich stream obtained from the purge gas from a methanol synthesis loop, which final mixture is then fed to the synthesis loop for methanol production. In order to achieve a stoichiometric ratio of hydrogen to carbon oxides, up to 50-60% of the entire feed needs to be subjected to steam reforming. This makes the steam reforming section of a methanol plant a considerable fraction of the investment of the entire plant. In addition, high steam reforming duty is also associated with significant fuel consumption by external burners in order to maintain the high temperatures required during steam reforming. This, in turn, leads to high CO2 emissions into the atmosphere.
It is therefore desired to provide a method for producing synthesis gas for methanol production, which process would be substantially devoid of the above disadvantages. Particularly, it is desired to have a process with a reduced fuel consumption and a reduced CO2 emission while producing synthesis gas having an optimal components ratio for methanol production.